The conventional obstacle determination device for vehicles is disclosed in JP-A-2006-117157 corresponding to US 2006/0087417 A1 as a pedestrian collision detecting device for detecting collision of a pedestrian or the like with a vehicle. The obstacle determination device includes an absorber, a pressure sensor, a velocity sensor and an airbag ECU device. The absorber is a member for absorbing an impact generated by collision of an object with a vehicle. The absorber includes a chamber member and a connection member. The chamber member is attached to a front surface of a bumper reinforcement by the connection member. Air is filled in a chamber which is provided by the chamber member. The pressure sensor detects a pressure inside the chamber. The pressure sensor is connected to the connection member through a tube. The velocity sensor is a sensor for detecting a velocity of the vehicle and arranged inside the vehicle. The pressure sensor and the velocity sensor are connected to the airbag ECU. The airbag ECU determines based on detecting results of the pressure sensor and the velocity sensor whether collision with a bumper of the vehicle is caused by a pedestrian. Specifically, the airbag ECU determines whether the pressure in the chamber exceeds a threshold value determined by a running velocity of the vehicle.
Standards of vehicles for North America require to have a structure of vehicles that breakage of the vehicle can be suppressed as much as possible even when the collision is caused. Thus, the absorber is made to be rigid. However, when the absorber is rigid, the chamber member is deformed only a little in case of collision is caused. That is, the deformation of the chamber member is limited. Therefore, it becomes difficult to change the pressure inside the chamber and it is difficult to determine the collision of the object with the vehicle accurately.